Tensile Drawing Research Articles

Tensile drawing of fully conjugated poly(2,5-thienylene vinylene)

A comparative study was made of mechanical and electrical properties of oriented poly(2,5-thienylene vinylene) (PTV) films prepared from the tractable precursor polymer poly[2,5-thienylene(1-methoxyethylene)] via two different processing routes. Materials were made both by the more common simultaneous tensile deformation and conversion method and by sequential conversion and drawing. It was found that both techniques yielded materials of identical, excellent conductivity and mechanical properties, provided that the fully converted PTV was oriented at significantly higher temperatures than the precursor polymer. Interestingly, the sequential conversion and drawing process proved to be the more efficient method. PTV films were obtained with Young's moduli of ∼7 GPa and electrical conductivities in excess of 10 3 S/cm, after doping with iodine.

Preparation and properties of ultra high molecular weight poly(ethylene terephthalate) fibers.

The preparation of ultra high molecular weight poly (ethylene terephthalate) (U-PET) and the drawing behavior of solution spun fibers from U-PET were investigated. U-PET was prepared by solidstate polymerization of porous and fibrous aggregates which were prepared from commercially available PET. As-spun fibers from U-PET (intrinsic viscosity, IV=3.6dL/g) were prepared by the solution spinning method using a mixed solvent of hexafluoro-2-propanol and dichloromethane (50/50, v/v). The polymer solution (8wt%) was extruded at room temperature through a conical capillary die with a diameter of 0.2mm. As-spun fibers were drawn at room temperature, followed by a tensile drawing at 210°C in an air. By this draw technique, the fibers could be drawn up to draw ratio of 12. Such highly drawn fibers exhibited tensile modulus and strength of 270 and 17g/d, respectively. However, the IV retention after the hot-drawing was only 67% primarily due to hydrolysis and/or oxidative degradation during processing.

Electrical and mechanical properties of oriented poly(3-alkylthiophenes): 2. Effect of side-chain length

The mechanical and electrical properties of solution-processed poly(3-alkylthiophenes) with alkyl side-chain lengths of 6, 8 and 12 carbon atoms are discussed. Tensile drawing at elevated temperatures yielded oriented materials with moderately increased mechanical properties. A simple model accounting for defects in the regiospecificity, i.e. head-to-tail versus head-to-head or tail-to-tail monomer coupling, is introduced, in addition to side-chain dilution, to account for the low moduli of undoped samples. Doping with FeCl 3 · 6H 2O led to significant enhancement of the mechanical properties of the drawn samples, as well as to high electrical conductivity. As was previously found for other conducting polymer systems, strong correlations were observed between mechanical properties and electrical conductivity. The conductivity was found to scale linearly with tenacity, independent of side-chain length.

An infra-red study of conformational changes occurring during the drawing of PEMT, PET and PEMT/PET copolymer

An i.r. study has been made of the conformational transitions which accompany the tensile drawing of poly(ethylene terephthalate) (PET) and the non-crystallizing polyesters, poly(ethylene methyl terephthalate) (PEMT) and a 60 40 PEMT/PET copolymer. For a given level of overall orientation, measured by birefringence, the gauche conformers were converted into trans more effectively and the trans conformers were more highly oriented in PET than in PEMT or the copolymer. The gauche/trans conformational change also occurred more effectively in hot drawing compared with cold drawing for PEMT and its copolymer. These differences in drawing behaviour were reflected in the development of elastic modulus with molecular orientation in these materials.

Tensile drawing behaviour of polyethylene terephthalate

AbstractA wide range of polyethylene terephthalate fibres was prepared by melt spinning to different degrees of molecular orientation. The tensile drawing behaviour of these fibers was then studied, either by drawing over a heated cylinder at 85°C or by drawing over both a heated cylinder and a plate at 180°C. The mechanical properties and structure of the subsequent drawn fibres are discussed in terms of the network draw ratio, determined by matching true stress–strain curves for the drawn and initial melt spun fibres. It is shown that this procedure provides valuable insight into subtle differences in properties and structure that can arise from differences in processing routes.

Mechanical and electrical properties of highly oriented polyacetylene films

An improved technique was developed for tensile drawing of polyacetylene films prepared by the non-solvent polymerization method of Akagi et al.; draw ratios as high as 15 were obtained. Tensile drawing and the associated orientation resulted in major improvement of both mechanical properties and the electrical conductivity (after doping). Maximum values for the modulus and tensile strength were 50 GPa and 0.9 GPa, respectively. The electrical conductivities of highly drawn thin films, doped with Iodine, along the orientation direction reached values at room temperature of up to 3×10 4 S/cm, with an anisotropy, σ ∥/ σ ⊥ > 250. The results demonstrate that the electrical conductvity increases linearly with the modulus and tensile strength, with polymer chain orientation as the implicit variable.

Mechanical and electrical properties of polyacetylene films oriented by tensile drawing

An improved technique was developed for tensile drawing of polyacetylene films prepared by the non-solvent polymerization method of Akagi et al.; draw ratios as high as 15 were obtained. Tensile drawing and the associated orientation resulted in major improvement of both the mechanical properties and the electrical conductivity (after doping). Maximum values for the modulus and tensile strength were 50 GPa and 0.9 GPa, respectively. The electrical conductivities of highly drawn thin films, doped with iodine, along the orientation direction reached values at room temperature of up to 3 × 10 4 S cm −1, with an anisotropy, σ ∥ σ ⊥ > 250 . Both Young's modulus and the tenacity decreased upon doping, typically by a factor of about 4–5, which is indicative of reduced intersegmental interaction. The results demonstrate that the electrical conductivity increases linearly with the modulus and tensile strength, with polymer chain orientation as the implicit variable.

Solid-state deformation of trans-1,4-polybutadiene

Abstract The uniaxial deformation behaviour of trans -1,4-polybutadiene was investigated. Trans -1,4-polybutadiene exhibits a solid-solid phase transition to a mobile pseudo-hexagonal, conformational disordered (condis), crystal structure at a temperature of approximately 65°C. Trans -1,4-polybutadiene cannot be deformed to high draw ratios via tensile drawing in the pseudo-hexagonal condis phase. Using coextrusion, trans -1,4-polybutadiene can be deformed, in the pseudo-hexagonal condis phase, to high (extrusion) draw ratios. Structures possessing a high degree of chain orientation in the extrusion direction and a strongly enhanced Young's modulus and tensile strength can be produced.

Thermal and mechanical behaviour of crystalline poly(ethylene terephthalate): effects of high temperature annealing and tensile drawing

The melting behaviour and several mechanical properties of crystallized poly(ethylene terephthalate) have been investigated paying particular attention to the effect of thermal annealing at high temperature. Although the occurrence of a double melting peak in the differential scanning calorimetry (d.s.c.) curves of isothermally annealed samples can be undeniably ascribed to a recrystallization process during the heating scan, it is suggested that the chain-folded lamellar crystals grown at a moderate crystallization temperature undergo a morphological change into fringed-micelle crystals when submitted to a high temperature annealing. This conclusion is inferred from the striking changes of the mechanical properties of the samples which result from the annealing treatment, in conjunction with the thermal behaviour of drawn samples. This metamorphosis is attributed to ester interchange reactions which turn the chain folds of the amorphous layers into intercrystalline tie molecules at high temperature.

Highly conductive and stiff fibres of poly(2,5-dimethoxy- p-phenylenevinylene) prepared from soluble precursor polymer

Fibres of poly(2,5-dimethoxy- p-phenylenevinylene), PDMPV, were prepared from a precursor polymer, poly[2,5-dimethoxy- p-phenylene (1-methoxyethylene)] which is soluble in organic solvents. Wet-spun precursor polymer fibres were drawn and converted to PDMPV in a temperature-controlled, continuous drawing system. X-ray diffraction patterns of the drawn PDMPV fibres indicated a high degree of molecular orientation with a mosaic spread less than 8°. Tensile drawing of PDMPV resulted in a dramatic improvement of the mechanical properties; at a draw ratio of 8, the modulus and strength were 35 GPa and 0.7 GPa, respectively. After doping (with iodine), the PDMPV fibres became highly conducting ( σ = 1200 S cm −1) while retaining excellent mechanical properties: the modulus decreased to 25 GPa and the tensile strength remained essentially unchanged. A strong correlation between the electrical conductivity and the mechanical properties was found.

Effect of molecular weight on drawing poly(vinyl alcohol) from solution-grown crystal mats

Solution-grown crystal (SGC) mats of poly(vinyl alcohol) (PVA) with different degrees of polymerization ( DP = 3 500–18 200), precipitated from dilute solutions in ethylene glycol, were drawn by solid state coextrusion followed by tensile drawing at elevated temperatures (two-stage drawing). The SGC mats exhibited significant strain hardening during the second-stage tensile drawing. The draw stress at a given draw ratio ( DR) was higher for higher DP samples. Although the draw stress decreased and the maximum achievable DR increased with increasing drawing temperature, the practically highest temperature was limited to ⩽220°C, due to thermal degradation at higher temperatures. The maximum DR thus achieved at 220°C, as well as the efficiency of draw evaluated by the thermal elastic shrinkage, was not significantly affected by the sample DP in the range studied in this work. The ambient tensile modulus and strength increased rapidly with DR up to 50 and 1.3 GPa, respectively, at the highest achieved DR of 20 for each DP, showing no significant effect of sample DP on either the drawability or the resultant tensile properties of drawn films. Thus, among several properties examined, only the draw and fracture stresses at elevated temperatures and the differential scanning calorimetry melting temperature of drawn samples were significantly affected by DP, being markedly higher for higher DP samples. These features in drawing SGC mats of PVA are markedly different from those previously observed in superdrawing of SGC mats of polyethylenes with different molecular weights.

Influence of chemical composition distribution and thermal history on the mechanical properties and viscoelastic relaxations of ethylene-1-butene copolymers

The tensile drawing behaviour and the dynamic mechanical properties of four ethylene-1-butene copolymers, with nearly the same comonomer content but obtained with slightly different catalyst systems, have been analysed. It was found that the large strain mechanical properties and the strain-hardening behaviour seem to be affected by the degree of homogeneity in the distribution of comonomer along the different chains, reflecting the differences in the catalyst systems used. However, a parallel trend was not so clear for the small-strain dynamic mechanical properties for a particular thermal history, although the dependence of the relaxations on the crystallization conditions is evident.

Mechanical and electrical properties of poly-(2,5-thienylene vinylene) fibers

Poly(2,5-thienylene vinylene) (PTV) fibers were prepared from a precursor polymer that is soluble in organic solvents. Fibers of the precursor polymer, poly[2,5-thienylene(1-methoxyethylene)], were wet spun from chloroform solutions. Tensile drawing and conversion (to the conjugated polymer) of the precursor polymer fibers were carried out with a continuous drawing system. Wide-angle X-ray diffraction patterns indicated a significant degree of molecular orientation of the drawn fibers. Tensile drawing and the associated extension and orientation of PTV resulted in major improvements in the mechanical properties of the pristine polymer fibers and the electrical conductivity (after doping with iodine). A linear correlation was found between the electrical conductivity and the modulus and tensile strength.

Effects of sample geometry and draw conditions on the mechanical properties of drawn poly(ethylene terephthalate)

Fibres and films prepared from solutions of high molecular weight poly(ethylene terephthalate) were drawn by two-stage drawing, tensile drawing or co-extrusion at low temperature (25–80°C) followed by tensile drawing at high temperature (230°C). Both fibres and films could be drawn up to a draw ratio of 11 by this method. The mechanical properties of drawn samples were greatly affected by the draw temperature for the first stage and the tension applied to the samples during cooling after the second-stage. The highest tensile modulus and strength for the drawn fibres that could be attained were 29.5 and 1.4 GPa, respectively, at the highest draw ratio of 11. For the films, the corresponding values were about half of those achieved for the fibres. The remarkable difference is closely related to the difference in amorphous chain orientation between drawn fibres and films, reflecting the different processing conditions available for each sample, and cross-sectional area.

Mechanical properties and dynamic mechanical relaxations of ethylene/alpha‐olefin copolymers

AbstractThe tensile drawing behaviour and the viscoelastic relaxations of three different copolymers of ethylene, containing 1‐butene, 1‐hexene and 4‐methyl‐1‐pentene as comonomer, have been studied. The composition of the copolymers is increasingly poorer in comonomer following the above order. However, they show similar mechanical properties, both large‐strain and small‐strain dynamic mechanical, because the minor differences which have been found can generally be explained by the thermal and mechanical histories of the samples. Thus, it seems that the higher disrupting effect produced in the copolymer structure by the comonomers of greater size and volume is counterbalanced by the corresponding smaller concentration, and that only thermal treatment produces appreciable differences in properties.

High strength/high modulus polyethylene: synthesis and processing of ultra-high molecular weight virgin powders

High strength/high modulus tapes and filaments were prepared directly from virgin ultra-high molecular weight (UHMW) polyethylene powders, by low temperature compression moulding and subsequent tensile drawing. We report in detail on the effects of various polymerization and compression moulding variables on the drawability of virgin UHMW polyethylene powders.

Study on the drawing behavior of poly(L‐lactide) to obtain high‐strength fibers

AbstractThe tensile drawing behavior of poly(L‐lactide) has been studied in order to obtain high strength fibers. Elongational viscosity measurements indicated that the hot drawing can take place in two temperature regions with different activation energies. Up to 180°C, the deformation proceeds in the semicrystalline state of the polymer having an activation energy of 15–28 kJ/mol, presumably by shear deformation. In the range of 180–190°C, the deformation proceeds in the liquid state of the polymer having an activation energy of 145–165 kJ/mol, leading to a semicrystalline state by strain hardening after displacement of topological defects. By using high deformation rates during drawing in a temperature gradient (tube drawing), the deformation will principally proceed in the semicrystalline region and inhomogeneous draw will take place leading to inferior fiber properties, unless the deformation rate and drawing temperature are strictly adjusted. Homogeneous drawing can be achieved by applying low deformation rates so that the deformation may take place in the liquid state of the polymer in which individual chains can be easily aligned and topological defects can be removed. Poly(L‐lactide) fibers with tensile strengths of 2.3 GPa have been produced in this way.

Processing, structure and properties of oriented polymers

AbstractThe fabrication techniques now available for the production of highly oriented polymers are reviewed. These techniques include tensile drawing from both melt‐spun and gel‐spun polymers, extrusion under pressure from the melt, and hydrostatic extrusion, ram extrusion and die drawing in the solid phase. In addition, lyotropic and thermotropic liquid crystalline polymers offer new routes to very stiff and strong polymers.Following the review of processing methods, an account is given of low strain mechanical behaviour and its relationship to structure, thermal properties (including thermal conductivity and thermal expansion behaviour) and barrier properties (permeability to liquids and gases and solubility).

Molecular deformation processes in an ethylene copolymer under tensile drawing: static and dynamic study by means of Fourier transform infra-red spectroscopy

Static and dynamic orientation measurements have been performed by means of Fourier transform infra-red spectroscopy in order to characterize the uniaxial drawing behaviour of an ethylene/1-butene copolymer. The orientational evolution of the crystalline bands in the static study has shown that the plastic deformation probably proceeds by untwisting of the original lamellar ribbons, before the onset of the fibrillar transformation. The assignment of some infra-red-active amorphous conformations with various kinds of chains has been discussed by considering their orientational behaviour. The dynamic study has revealed relaxation processes of the amorphous chains together with strain-induced crystallization, in a range of time up to a few tens of milliseconds after neck completion.

Effects of initial morphology and molecular weight on the deformability of poly(ethylene terephthalate)

AbstractSolution‐grown crystal (SGC) mats and solution‐cast (SC) films of poly(ethylene terephthalate) (PET) were drawn by solid‐state coextrusion followed by tensile drawing of the coextrudates. Drawabilities and properties of the drawn films, such as mechanical and thermal properties, were investigated as functions of molecular weight, initial morphology, and drawing conditions. The initial morphology and molecular weight have a marked effect on the drawability and tensile properties of the resultant drawn films. The attainable maximum draw ratio increases with increasing molecular weight, and the highest draw ratio of 11.5 can be achieved by two‐stage drawing of SC films prepared from pellets with an intrinsic viscosity of 1.43 dl/g. Such highly drawn films exhibit a tensile modulus of 17.5 GPa and strength at break of 400 MPa. These values are comparable to those obtained in conventional spinning of standard grade PET. At a given draw ratio, the tensile strength of the drawn films increases with increasing molecular weight, but the molecular weight dependence is not so marked in the tensile modulus as in the tensile strength. At a given molecular weight, the drawability of SGC mats is lower than that for SC films; however, the efficiency of drawing is higher for the former than for the latter. The difference may arise from the difference in crystallinity and/or crystal perfection of predrawn samples.